The present invention relates to a method of treating a damaged foul release coating area on a metallic substrate, such as the surface of a ship's hull, with an organosilicon adhesion promoter composition. The application of a duplex silicone foul release coating system is made feasible after the organosilicon adhesion promoter composition is applied.
Metallic structures submerged in sea water, such as ship bottoms, are generally infested with organisms, such as barnacles, tube worms, and algae, which can become attached to the surface of these structures causing increased fuel consumption due to increased drag. Routinely, anti-fouling paints are used to treat the surface of these exposed substrates to minimize fouling attachments. Silicones have been known as effective anti-fouling coatings as early as the 1970's, as shown by U.S. Pat. Nos. 4,025,693, 4,080,190 and 4,227,929.
While silicones are recognized as effective anti-fouling coatings when in contact with sea water, silicones do not possess the anti-corrosion resistance of various organic materials, such as epoxy resins. As a result, an anti-corrosive epoxy coating is usually applied under ambient conditions onto a metallic surface of a ship's hull after it has been previously sanded to expose metal surface. Subsequent treatment with an anti-fouling coating, such as a silicone, generally requires a tie-coat to bond the silicone to the epoxy surface.
In Griffith, U.S. Pat. No. 5,449,553, which is incorporated herein by reference, a nontoxic anti-fouling system is described which involves the use of duplex silicone foul release coatings. One of the silicone coatings is a room temperature vulcanizable (RTV) composition, such as, GE RTV 11. The RTV composition is applied onto a semi-cured bonding layer which in turn can be applied onto an epoxy coating. Among the ingredients in the semi-cured bonding layer, there is included a reaction product of a hydroxy-terminated organopolysiloxane and a polymerizable monomer, such as styrene, or a conjugated diolefin, for example 1,3-butadiene. The hydroxy-terminated organopolysiloxane reaction product is combined in the absence of moisture with a partial hydrolysis product of ethyl silicate and dibutyltin butoxychloride to form a condensation cure RTV composition.
Griffith, U.S. Pat. No. 5,449,553, also shows a related semi-cured bonding layer composition referenced as Silgan J-501 of the Wacker Silicones Corporation of Adrian, Mich. Silgan J-501, also can be applied directly onto an epoxy-treated steel substrate, such as a ship's hull, and can serve as an anchor for a subsequently applied exterior silicone RTV release layer. The combination of these RTV's, which can be included under the expression "duplex silicone foul release system" has been found to be effective as a foul release system when properly secured to a ship's hull, and more particularly, to an epoxy-coated steel hull.
Experience has shown however, that while adhesion is generally satisfactory between the respective cured silicone layers, namely the silicone RTV foul release coating, and the aforementioned silicone-organic bonding layer, adhesion between the silicone bonding layer and the epoxy coating on the ship's hull requires an epoxy containing "tackcoat". As a result, a satisfactory foul release coating system for a ship's hull generally requires a multi-tier coating system consisting of an initial anti-corrosive epoxy coating, an epoxy tack or mistcoat, a silicone bonding layer, and a silicone foul release topcoat which is in direct contact with sea water. Further, satisfactory adhesion of the silicone RTV foul release topcoat generally requires a freshly applied silicone bonding layer.
As a result, if a ship suffers peripheral damage to its hull, even in a limited area, which can result in the penetration or destruction of one or more of the multi-tier silicone-epoxy coating layers, a complicated, or formidable repair procedure is often necessary. For example, restoration of the multi-tier silicone-epoxy coating layers may require the reapplication of the original anti-corrosive epoxy coating onto freshly sanded steel surface, followed by treating the epoxy layer with a tie-coat, and thereafter the application of the dual silicone foul release coating system.
It would be desirable therefor to provide a simpler patching, or repair process to allow the direct application of the duplex silicone foul release system onto the damaged area of the ship's hull in an effective manner.